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  • QTL  (100)
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  • 1
    ISSN: 1432-2242
    Keywords: Key words Beta vulgaris ; Cercospora beticola ; AFLP ; QTL
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The breeding of sugar beet varieties that combine resistance to Cercospora and high yield under non-diseased conditions is a major challenge to the breeder. The understanding of the quantitative trait loci (QTLs) contributing to Cercospora resistance offers one route to solving this problem. A QTL analysis of Cercospora resistance in sugar beet was carried out using a linkage map based on AFLP and RFLP markers. Two different screening methods for Cercospora resistance (a field test at Copparo, Italy, under natural infection, and a newly-developed leaf disc test) were used to estimate the level of Cercospora resistance; the correlation between scores from the field (at 162 days after sowing) and the leaf disc test was significant. QTL analysis was based on F2 and F3 (half-sib family) generations derived from crosses between diploid single plants of 93164P (resistant to Cercospora leaf spot disease) and 95098P (susceptible). Four QTLs associated with Cercospora resistance (based on Lsmean data of the leaf disc test) on chromosomes III, IV, VII and IX were revealed using Composite interval mapping. To produce populations segregating for leaf spot resistance as a single Mendelian factor, we selected for plants heterozygous for only one of the QTLs (on chromosome IV or IX) but homozygous for the others.
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  • 2
    ISSN: 1432-2242
    Keywords: Keywords Domestication ; Evolution ; QTL ; Map-based cloning ; Lycopersicon esculentum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The seeds of domesticated plants are normally much larger than those of their wild counterparts. This change in seed weight was most likely in response to the selection pressure for yield, uniform germination and seedling vigor which was exerted by humans during domestication. However, despite the evolutionary and agronomic significance of seed weight, very little is know about the genetic and developmental controls of this trait; and, thus far, none of the genes in this pathway have been isolated from any plant species. QTL mapping experiments conducted in tomato during the past decade have allowed the identification of many seed-weight QTLs and have also revealed that only a few loci are responsible for the majority of the seed-weight changes that accompanied the domestication of tomato. This review presents a consensus map for seed weight QTL identified in previously published reports and in unpublished results from our laboratory. This summary of seed-weight QTL data allows for the identification of the major loci controlling this trait in the genus Lycopersicon. It is hoped that this work will allow the elucidation of this important phenotypic transition that occurred during crop-plant domestication and will also provide the starting point for the cloning of a gene responsible for seed-weight variation.
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  • 3
    ISSN: 1432-2242
    Keywords: Key words Barley ; Genome mapping ; Stripe rust ; Leaf rust ; BYDV ; Resistance Gene Analog Polymorphism ; QTL
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Stripe rust, leaf rust, and Barley Yellow Dwarf Virus (BYDV) are important diseases of barley (Hordeum vulgare L). Using 94 doubled-haploid lines (DH) from the cross of Shyri x Galena, multiple disease phenotype datasets, and a 99-marker linkage map, we determined the number, genome location, and effects of genes conferring resistance to these diseases. We also mapped Resistance Gene Analog Polymorphism (RGAP) loci, based on degenerate motifs of cloned disease resistance genes, in the same population. Leaf rust resistance was determined by a single gene on chromosome 1 (7H). QTLs on chromosomes 2 (2H), 3 (3H), 5 (1H), and 6 (6H) were the principal determinants of resistance to stripe rust. Two- locus QTL interactions were significant determinants of resistance to this disease. Resistance to the MAV and PAV serotypes of BYDV was determined by coincident QTLs on chromosomes 1 (7H), 4 (4H), and 5 (1H). QTL interactions were not significant for BYDV resistance. The associations of molecular markers with qualitative and quantitative disease resistance loci will be a useful information for marker-assisted selection.
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  • 4
    ISSN: 1432-2242
    Keywords: Key words Sunflower ; Helianthus annuus L. ; AFLP ; QTL ; Protoplast ; In vitro regeneration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Experiments were conducted to identify the genetic factors controlling protoplast division and to determine eventual relations between genetic factors involving organogenesis, somatic embryogenesis and protoplast division in sunflower. The present study involved protoplast culture and two traits: total division per 100 protoplasts (TOTD) and asymmetric division per 100 protoplasts (ASYD) were scored in 52 recombinant inbred lines (RILs) from a cross between PAC-2 and RHA-266. Asymmetric division is an early event in the formation of embryoids from protoplasts. Analysis of variance indicated the existence of highly significant differences among parental genotypes and their RILs. Heritability for the two protoplast division parameters (TOTD and ASYD) was high (0.87 and 0.89, respectively) and genetic gain expressed as percentage of the best parent for 10% of the selected RILs was significant. Twelve putative loci associated with total division per 100 protoplasts were identified. Eleven QTLs were also detected for asymmetric division per 100 protoplasts. The QTLs present high significant LOD scores and sum to a high percentage of phenotypic variance. The percentage of phenotypic variation explained by each QTL ranged from 2% to 24%. Some segments of the linkage groups I, XV and XVII are likely to contain genes important for organogenesis, somatic embryogenesis and protoplast division, as clustering of QTLs for these characters were described. The QTLs identified in these three linkage groups should be involved in cell division and in early events associated with cell differenciation.
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  • 5
    ISSN: 1432-2242
    Keywords: Key words Brittle rachis ; Weak rachis ; QTL ; Spike density ; Peduncle curvature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Head shattering in barley (Hordeum vulgare L.) has two forms; brittle rachis and weak rachis. Brittle rachis is not observed in cultivated barley since all cultivars carry non-brittle alleles at one of the two complementary brittle rachis loci (Btr1;Btr2). Weak rachis causes head shattering in barley cultivars and may be confused with brittle rachis. Brittle rachis has been mapped to the chromosome 3 (3H) short arm while map position(s) of the weak rachis is unknown. Two major and a putative minor QTL for head shattering were mapped using the Steptoe × Morex doubled haploid line population. The largest QTL, designated Hst-3, located on the chromosome 3 (3H) centromeric region, is associated with a major yield QTL. The Steptoe Hst-3 region, when transferred into Morex, resulted in a substantial decrease in head shattering. High-resolution mapping of Hst-3 was achieved using isogenic lines. Brittle rachis was mapped with molecular markers and shown to be located in a different position from that of Hst-3. The second major QTL, designated Hst-2 S, is located on chromosome 2 S. This locus is associated with an environmentally sensitive yield QTL.
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  • 6
    ISSN: 1432-2242
    Keywords: Key words Oryza sativa L. ; Ratoon ; Molecular marker ; QTL
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Although F2s are the most informative populations for genetic analysis, it has been difficult to use F2 populations directly for QTL analysis because it is usually difficult to assess the reliability of the data, due to an inability to estimate the experimental errors. In this study, we performed a QTL analysis for yield and yield-component traits of an F2 population based on data from replicated field trials over 2 years using vegetative shoots of ratooned plants, making use of the ratooning habit of rice. The objective of this study was to explore the possibility of conducting QTL analyses directly based on an F2 population by means of ratooning plants. The experimental population was from a cross between ’Zhenshan 97’ and ’Minghui 63’, the parents of ’Shanyou 63’, an elite rice hybrid widely grown in China. A genetic linkage map containing 151 molecular markers was constructed for QTL mapping. A total of 20 distinct QTLs were detected; eight of these were detected in both years and remaining 12 in only 1 year. Compared with the results of our previous analysis of the F2:3 families from the same cross, it was shown that most of the QTLs detected in the ratooned F2 population were also detected in the F2:3 population. However, the estimates of both additive and dominant types of genetic effects for many of the QTLs based on F2 ratoons were substantially larger than those based on F2:3 families. The results indicate that vegetatively ratooned F2 populations may have considerable utility in the mapping of QTLs, especially if dominant types of gene actions are of concern, although there were certain technical limitations in making use of such populations in the experiments.
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  • 7
    ISSN: 1432-2242
    Keywords: Key words Rice ; Bacterial leaf streak ; Mapping ; Bulked segregant analysis ; QTL
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  A large F2 and a RI population were separately derived from a cross between two indica rice varieties, one of which was highly resistant to bacterial leaf streak (BLS) and the other highly susceptible. Following artificial inoculation of the RI population and over 2 years of testing, 11 QTLs were mapped by composite interval mapping (CIM) on six chromosomes. Six of the QTLs were detected in both seasons. Eight of the QTLs were significant following stepwise regression analysis, and of these, 5 with the largest effects were significant in both seasons. The detected QTLs explained 84.6% of the genetic variation in 1997. Bulked segregant analysis (BSA) of the extremes of the F2 population identified 3 QTLs of large effect. The 3 QTLs were dentical to 3 of the 5 largest QTLs detected by CIM. The independent detection of the same QTLs using two methods of analysis in separate mapping populations verifies the existence of the QTLs for BLS and provides markers to ease their introduction into elite varieties.
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  • 8
    ISSN: 1432-2242
    Keywords: Key words Lycopersicon esculentum ; Lycopersicon hirsutum ; Chilling tolerance ; QTL ; Shoot wilting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The genetic basis for shoot wilting and root ammonium uptake under chilling temperatures was examined in an interspecific backcross (BC1) population derived from Lycopersicon esculentum Mill. cv T5 and wild Lycopersicon hirsutum f. typicum accession LA1778. The chilling sensitivity of shoot wilting and ammonium uptake was evaluated in four replicated cuttings from each of 196 BC1 plants. Wilting was evaluated at two different times: 2 hours (wilting 2 h) and 6 hours (wilting 6 h recovery) after root exposure to 4°C. The BC1 plants were genotyped with 89 polymorphic RFLP markers, and composite interval mapping was used to detect quantitative trait loci (QTLs). Three QTLs, one each on chromosomes 5, 6 and 9, were detected for wilting 2 h. The presence of a L. hirsutum (H) allele at the QTL on chromosomes 5 and 9 decreased wilting, while the H allele at the QTL on chromosome 6 increased wilting. To analyze plant recovery from wilting at 6 h, subsets of the BC1 population were selected, based on phenotype and genotype, because not all plants wilted at 2 h. The phenotype subset (wilting 6 h-PS) included plants that wilted to a greater degree at 2 h, and the genotype subsets included plants carrying specific allelic compositions at the QTL for wilting 2 h on chromosomes 5 (wilting 6 h-GS-ch5), 6 (wilting 6 h-GS-ch6), and 9 (wilting 6 h-GS-ch9). On chromosome 6, a QTL was located that was associated with three subsets (wilting 6 h-PS, wilting 6 h-GS-ch5 and wilting 6 h-GS-ch9), while on chromosome 7 a QTL was detected with two subsets (wilting 6 h-PS and wilting 6 h-GS-ch5). Three additional QTLs were detected within a single subset: chromosome 1 (wilting 6 h-GS-ch6), chromosome 11 (wilting 6 h-GS-ch5) and chromosome 12 (wilting 6 h-GS-ch9). The presence of the H allele at the QTL on chromosomes 7 and 12 had a positive effect, enhancing recovery from wilting, while the H allele at the other QTL had a negative effect. Three traits were used to evaluate the chilling sensitivity of root ammonium uptake: ammonium uptake before a chilling episode, ammonium uptake after the chilling episode, and the relative inhibition of uptake (difference in uptake rates before and after chilling divided by the rate before chilling). One QTL was detected on chromosome 3 for the rate before chilling and one on chromosome 6 for the relative inhibition of ammonium uptake. Our results demonstrate that shoot wilting and ammonium uptake under chilling are controlled by multiple QTLs.
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  • 9
    ISSN: 1432-2242
    Keywords: Inbred lines ; QTL ; Epistasis ; Body weight
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary It is shown that the heterogametic sex of crosses between two highly inbred lines of animals provides a simple means to detect large effects of specific sex chromosomes on quantitative traits. Linear combinations of adjusted trait averages of matching types of crosses between three inbred lines of chickens were used to investigate sex chromosome effects. Evidence for a large influence of the W chromosome of one line on body weight was found. Estimated effects were between 2.4 and 7.2% of the corresponding phenotypic means. The autosomal genetic background exhibited a strong influence on the effect, thus suggesting a sizable amount of epistasis (interaction between sex chromosomes and genetic background).
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  • 10
    ISSN: 1432-2242
    Keywords: Molecular markers ; Epistatic effects ; RFLP ; Linkage ; QTL
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The development of molecular markers has recently raised expectations for their application in selection programs. However, some questions related to quantitative trait loci (QTL) identification are still unanswered. The objectives of this paper are (1) to develop statistical genetic models for detecting and locating on the genome multi-QTL with additive, dominance and epistatic effects using multiple linear regression analysis in the backcross and Fn generations from the cross of two inbred lines; and (2) to discuss the bias caused by linked and unlinked QTL on the genetic estimates. Non-linear models were developed for different backcross and Fn generations when both epistasis and no epistasis were assumed. Generation analysis of marked progenies is suggested as a way of increasing the number of observations for the estimates without additional cost for molecular scoring. Some groups of progenies can be created in different generations from the same scored individuals. The non-linear models were transformed into approximate multivariate linear models to which combined stepwise and standard regression analysis could be applied. Expressions for the biases of the marker classes from linked QTL were obtained when no epistasis was assumed. When epistasis was assumed, these expressions increased in complexity, and the biases were caused by both linked and unlinked QTL.
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